The invention relates to maintenance of quality in a mobile telephone network and especially to measurement of radio path quality and coordinates of a measuring point at an arbitrary point of the network.
FIG. 1 shows those parts of a mobile station system which are substantial for the invention. A mobile station MS communicates by radio with a base station BTS. One or several base stations BTS form together with a base station controller BSC a base station subsystem BSS, which again is connected to a mobile telephone network PLMN. The quality of the services produced by the network is monitored in a network management subsystem NMS and, to be precise, in an operation and maintenance centre OMC therein. The broken lines in FIG. 1 represent interfaces crossed by signals. Signals between the mobile station MS and the base station BTS propagate over air interface. The base station subsystem BSS communicates with the network subsystem over A interface. The management subsystem NMS communicates with the rest of the network over operation and maintenance interface O&M.
Signals do not always propagate straight between an antenna ANT of a base station BTS and a mobile station MS. The propagation of signals is interfered e.g. by attenuations caused by terrain form and buildings, reflections from even surfaces, such as walls of buildings. When signals arriving along different paths are summed in a receiver, it can be observed that the signal strength as a function of the distance of the receiver reaches several minimum points at distances of almost one wavelength from each other. The phenomenon is called Rayleigh fading, i.e. multipath fading. See e.g. Mouly-Pautet: "The GSM System for Mobile Communications", FIG. 4.19 with explanation. Other interfering factors are for instance narrow-band interferences from other mobile stations MS and broadband interferences from electric systems of cars or from lightnings, for instance. In addition, rain attenuates radio signals.
For monitoring the signal quality in a mobile telephone network, the following parameters among others are used: signal strength, bit error ratio BER and propagation time, on the basis of which a timing advance is formed. Within the scope of this application, these parameters associated with signal quality are combined to a concept `signal quality` SQ. In the exemplifying GSM system, both the mobile station and the base station measure the above three parameters. The mobile station measures the signal strength in that base station where it is locked and, in addition to that, in adjacent base stations.
In general, parameters associated with signal quality are functions of location and also of time. One problem with mapping shadow regions conists of precision requirements with respect to location determination. Due to multipath fading, particularly, the signal strength varies considerably along a distance as small as one wavelength (about 30 cm). It is known to provide important measuring points of the network with special measuring telephones, which give the network feedback concerning signal quality. A problem with such fixed measuring telephones is that they can measure network parameters only at predetermined fixed points. For example, fixed telephones are not capable of measuring how a handover succeeds.
PCT Publication WO 93/15569 (PCT/US93/00579, Franza et al.) discloses a partial solution to the above problems. However, this solution involves certain problems. Firstly, the equipment is big and it is suggested to be located in a delivery van, for instance. This leads to the problem that radio path quality values of a network can be measured only at places which are accessible by a car or a delivery van. Indoor spaces of buildings, public vehicles, subway tunnels, pedestrian streets, recreational areas and water areas etc. are areas where no measurements can be performed by means of the system according to said WO Application. Another problem, which is not solved by the system according to this PCT Application, consists in combining measurement results from an uplink transmission path and a downlink transmission path. On page 8 of said WO Published Application, it says that "The data accumulated by the computer in the base station and the computer on the mobile platform may be stored and later combined". This later combining is problematic per se, because it requires additional calculation. The results from the uplink transmission path of a predetermined measuring device have to be combined with the results from the downlink transmission path of the same measuring device. This combining also causes delays in the maintenance of the network. If the measurement results from the uplink transmission path are poor, the user of the measuring device does not know that and cannot concentrate measurements on problematic places. Still another problem caused by a later combining is that it is not possible until after the combining to make a final decision on whether some measuring event involves something abnormal due to which the measurement result should be stored for a later analysis.